1. Field of the Invention
This invention relates to cylinder locks and particularly to pin tumbler cylinder locks with axial sliding detainers that provide a secondary locking mechanism in the cylinders.
2. Discussion of the Background
An ongoing problem for people using locks is other people trying to pick these locks. Pin tumbler locks, a traditional type of lock, are so common that one can buy tools specifically designed to pick a pin tumbler lock. At the same time, pin tumbler technology is well known, and consumers are comfortable with pin tumbler keys. As described below, many have looked to develop an improved lock that is less susceptible to lock picking.
A. Sohm in U.S. Pat. No. 1,141,215 discloses a cylinder where the plug contains moveable wards, or sliders, that are pushed axially by the insertion of the key. The sliders have a key contact surface and a projecting blade that extends into the shell. The shell contains annular grooves that will accept the projecting blade when the sliders are correctly positioned by the key. When the blades are positioned within the annular grooves, the plug is free to turn.
The moveable wards or sliders of this invention are primary locking elements in the cylinder. They also directly block the rotation of the plug within the shell.
B. Perkut in German Pat. No. DE 2 828 343 teaches two locking concepts. The first one (see FIG. 5) is of a moveable ward or slider that is very similar to the Sohm patent, but is used as a secondary locking mechanism in a pin tumbler cylinder. The slider 12′ has a blade 34 that extends into the shell and must be pushed by the key to an unlocked position, whereupon the blade is located in an annular ring 38 in the shell. This slider directly blocks the rotation of the plug within the shell.
The second locking concept (see FIGS. 1-4) also uses the slider as an auxiliary locking mechanism. The slider 12, interfaces with a ball 20 that extends from the plug into the shell and blocks the rotation of the plug. The slider has a cavity 18 that will accept the ball when the slider is pushed to a correct axial position. When both the primary tumbler pins 106a and 106b and the slider are correctly aligned, the rotation of the plug forces the ball out of the shell into the plug and into the cavity 18 in the slider. Thus the plug can rotate freely. This slider provides an intermediary member, the ball, to block the rotation of the plug within the shell. However the curved shape of a ball will allow the plug to turn even if the slider is not precisely positioned.
G. Brandt in U.S. Pat. No. 5,615,566 also discloses a cylinder where the plug contains an auxiliary locking element, or slider, in addition to the regular pin tumblers. The Brandt slider 16 has a projecting blade 54 that extends out the back side of the plug and fits into a notch 24 in the shell. When the slider is pushed to the rear-most position by the insertion of the key, the slider is pushed out of the notch in the shell, and if the tumbler pins are also correctly aligned, the plug is free to rotate. The slider directly blocks the plug from rotating within the shell.
P. Field et al. in U.S. Pat. No. 6,477,875 discloses a cylinder where the plug contains sliders 24 or 24′ that move axially and provide tertiary locking mechanisms in the cylinder. The rotating pins must be correctly elevated for the shear line and also be rotationally aligned for the sidebar mechanism 16 or 16′ before the cylinder will unlock. Additionally, the sliders in the Field invention have projecting blades 32 or 32′ that are used to block the sidebar mechanism. The slider must be positioned at the correct axial location before the sidebar can contact the rotating pins. This slider blocks the motion of the sidebar in the plug.
Additional detailed specifications of a sidebar cylinder with a P. Field et al. slider and the key interface is provided in U.S. Pat. No. 6,945,082.
B. Field et al. in U.S. Pat. Application Publication 2007/0137272 teaches a cylinder that contains a sidebar 18 that is axially positioned by the side of a key. When moved to the correct position, the ends of the sidebar are at a location to allow the sidebar to cam into the plug and contact the side of the keyblade. If the key blade is configured with a shape corresponding to the edge of the sidebar 36, the sidebar can move and allow the plug to rotate. The sliding sidebar directly blocks rotation of the plug in the shell.
The inventor has found that these lock designs have room for improvement. In particular, these additional mechanisms require valuable space within a traditional pin and tumbler design, and thus require that locks incorporating these features must be large or, alternatively, if a large lock is not possible, these features must be foregone.